ACTIVITIES OF COLONIAL ANIMALS 491 
nevertheless I believe it to be true. It probably rests upon a 
natural daily rhythm in the animal’s metabolism. Phosphor- 
escence induced during the daytime by placing a colony for an 
hour or so in the dark is completely lost on exposure to daylight 
for about five minutes. If during the night a colony that shows 
a naturally acquired bright phosphorescence is illuminated by a 
strong electric light (40-watt Mazda lamp at 40 cm. distance), 
the ability to produce light steadily decreases. After five min- 
utes’ exposure to light the phosphorescence of the Renilla was 
obviously fainter than that of another kept in the dark as a 
check. And after ten minutes’ exposure it was very faint in 
comparison. Continued exposure, however, never totally oblit- 
erated the light, showing that either electric light is not so effec- 
tive in this respect as daylight or that during the night Renilla 
is more efficient in producing those substances necessary for the 
production of light than during the daytime. Renilla is then 
like certain other marine organisms, ctenophores for instance 
(Peters, ’05), which become capable of phosphorescence only in 
the dark and lose this capacity more or less completely in the 
light, especially in daylight. 
Renilla is phosphorescent only on stimulation. If in the night- 
time a spot on the superior surface of the rachis is stimulated 
mechanically by being prodded or pinched or excited by a faradic 
current, a series of luminous ripples emanate from it and spread 
concentrically over the rachis like waves over the smooth surface 
of a pond into which a pebble has been thrown. If a fine needle 
point is used as a mechanical stimulus, a single point of light can 
be excited on the rachis, and this point will glow for some sec- 
onds and without becoming a center from which waves emanate, 
thus showing that in this instance the activity is strictly local. _ 
Although the phosphorescence of Renilla can easily be excited 
by mechanical stimulation, it is noteworthy that the rachidial 
waves, which were often found running on Renilla in the night 
and must have produced considerable mechanical disturbance, 
never excited phosphorescence. If, however, a specimen on 
which rachidial waves were running was even gently prodded 
with a rod, waves of phosphorescence would sweep over it unin- . 
terruptedly even while the rachidial wave was in progress. 
